The invention relates to an onboard power supply system for a motor vehicle and to a method and a device for operating the onboard power supply system.
In modern motor vehicles, high demands are made on an electric onboard power supply system with an electric energy accumulator (storage device), particularly in the case of motor vehicles capable of converting kinetic energy of the motor vehicle, for example, within the scope of a braking operation, to electric energy and returning it to the energy accumulator.
It is an object of the invention to create an onboard power supply system of a motor vehicle and a method and a corresponding device for operating the onboard power supply system which permits an efficient operation of consuming devices.
This and other objects are achieved in accordance with the invention. According to a first aspect of the invention, an onboard power supply system for a motor vehicle includes a voltage converter having a first connection and a second connection. The onboard power supply system also includes a voltage source which is electrically coupled with the first connection of the voltage converter and is constructed for providing a predefined source voltage. Furthermore, the onboard power supply system includes a base energy accumulator which, by way of its first connection, is electrically coupled with the second connection of the voltage converter and, by way of its second connection, is electrically coupled with the reference potential and is constructed for providing a predefined base voltage. With respect to the amount, the source voltage of the voltage source is greater than the base voltage. Furthermore, the onboard power supply system has at least one first selection circuit of at least one first electrical consuming device which is arranged so that it can be electrically coupled parallel to the voltage converter. The onboard power supply system also has at least one second selection circuit of at least one second electrical consuming device which is arranged so that it can be electrically coupled parallel to the base energy accumulator.
Such an onboard power supply system permits a particularly power-loss-reduced operation. In particular, power loss allocated to the voltage converter is reduced in that at least a portion of a current for operating the coupled and switched-on consuming devices is not guided by way of the voltage converter, but is preferably fed directly from the voltage source and/or the base energy accumulator to the corresponding consuming devices. If the source voltage is approximately twice as large as the base voltage, the at least one first selection and the at least one second selection is, in each case, acted upon by approximately the same voltage. The voltage assigned to the at least one first selection is a result of a difference between the source voltage and the base voltage. The source voltage and the base voltage are in each case preferably a direct voltage.
The voltage converter may, for example, be constructed as a voltage regulator, thus, for example, as a switching regulator. It may also be constructed, for example, as a unidirectional transformer and therefore provide the base voltage and/or a base current as a function of the source voltage at the first connection on the output side at its second connection. This contributes to the fact that undervoltages at the second connection are compensated. However, the voltage converter may, for example, also be constructed as a bidirectional transformer and, in addition to the unidirectional transformer, also as a function of the base voltage at the second connection, provide the source voltage and/or a source current at the first connection. In this case, overvoltages at the second connection may preferably also be compensated by way of the bidirectional voltage converter. This permits a balancing to the extent that, for example, the first selection and the second selection are in each case acted upon by approximately identical voltages.
The at least one first consuming device of the first selection and the at least one second consuming device of the second selection are constructed so that they can be switched on and off and are thereby acted upon by the respective voltage as a function of their switching condition. High-current consuming devices, for example, such as a starting system, can be assigned to the first selection. A power consumption of the first selection is preferably lower than a power consumption of the second selection. Particularly when a unidirectional voltage converter is used, this can contribute to the fact that energy required for operating the second selection is transmitted from the first connection to the second connection of the voltage converter. If the power consumption of the first selection is lower, the latter, as required, can be operated only to a limited extent or not at all, particularly when a unidirectional voltage converter is used which transmits electric energy from its first connection to its second connection. This can be made possible particularly by the use of a bidirectional voltage converter.
The energy accumulator may be constructed, for example, as a lead accumulator, in which case other constructions can also be used.
In a further advantageous development of the first aspect, the voltage source includes an additional energy accumulator and/or a generator for providing the source voltage. The generator may, for example, be a generator of the motor vehicle. The additional energy accumulator is, for example, constructed as a li-ion accumulator and, in motor vehicles, particularly hybrid vehicles, which have an energy recovery device, thus, for example, during a braking operation, can be called a recuperation accumulator. The generator is operated at least temporarily during an operation of the motor vehicle in order to approximately provide the source voltage, the source voltage also including a voltage provided by the generator for permitting a reliable charging of the additional energy accumulator and/or of the base energy accumulator. The generator can also be operated during a recuperation phase, i.e., during an energy feedback, for example, during the braking operation or during a coasting operation of the motor vehicle in order to, for example, convert kinetic energy of the motor vehicle to electric energy. The generator can, for example, also be constructed as a starter generator and thereby can also be used for starting an internal-combustion engine of the motor vehicle. When both components are present, the generator is preferably electrically coupled parallel to the additional energy accumulator.
According to a second aspect, the invention is characterized by an onboard power supply system for a motor vehicle that has an energy accumulator and a base energy accumulator. The two energy accumulators are electrically connected in series. The energy accumulator is constructed for providing a predefined voltage. The base energy accumulator is constructed for providing a predefined base voltage. The onboard power supply system also has a voltage source which can be electrically coupled with the energy accumulator and is constructed for providing a source voltage. The source voltage is approximately as large as a sum of the voltage and the base voltage. Furthermore, the onboard power supply system has at least one first selection of at least one first electric consuming device which is arranged so that it can be electrically coupled parallel to the energy accumulator. Furthermore, the onboard power supply system has at least one second selection of at least one second electric consuming device which is arranged so that it can be electrically coupled parallel to the base energy accumulator.
This makes it possible to obtain a particularly simple and cost-effective onboard power supply system with a power-loss-reduced operation. In particular, a portion of a current for operating the coupled and switched-on consuming devices is not conducted by way of the base energy accumulator but preferably directly from the voltage source and/or the energy accumulator. The voltage source preferably includes only the generator for providing the source voltage.
In an advantageous further development of the first and the second aspect, one of the first selections is assigned to one of the second selections, specifically such that the respective first selection has approximately the same power consumption as the assigned second selection. The first selection has a predefined number of first electric consuming devices, and the second selection has a predefined number of second electric consuming devices, in which case also only one corresponding electric consuming device may be assigned to the first selection or to the second selection. The first and assigned second selection thereby represents an approximately symmetrical load. This has the advantage that source current essentially flows through the first and assigned second selection, whereby the voltage converter and/or the base energy accumulator can be relieved.
Generally, more than one first selection and more than one second selection may also be present.
In a further advantageous development of the first and second aspect, the respective first selection and the assigned second selection are predefined such that both have approximately the same time-related progression of the power consumption. This can take place, for example, in that the at least one first consuming device of the first selection and the at least one second consuming device of the assigned second selection can be switched on and off approximately isochronously. This makes it possible to obtain a symmetrical load and a power-loss-reduced operation of the onboard power supply system. Consuming devices of the respective selection can also be predefined which also have different power consumptions at different points in time during their operation.
In a further advantageous development of the first and second aspect, the onboard power supply system has at least one additional consuming device which can be electrically coupled parallel to the voltage source. Also, this arrangement of the at least one further electric consuming device can contribute to the fact that a current provided by the voltage converter and/or base energy accumulator can be reduced. In particular, this results in a reduced current demand from the voltage source because the at least one additional consuming device is operated at the source voltage whose amount is larger than that of the base voltage. Preferably, voltage-insensitive loads, such as the seat heaters, and the rear window heater, the steering system, can be used as additional consuming devices.
At least one safety-critical electric consuming device respectively is preferably assigned to the first selection and/or the second selection.
According to a third and fourth aspect, the invention is characterized by a method and a corresponding device for operating an onboard power supply system according to the first aspect, by which faults in line sections assigned to the voltage converter, and/or of the voltage converter itself, are detected. As a function of the detection, the consuming device or the first consuming devices of at least one of the at least one first selection are switched on. This has the advantage that the base energy accumulator can continue to be charged by way of the at least one switched-on first selection. In addition, it is possible to operate at least one second electric consuming device or at least one second selection. This permits a particularly reliable operation of the motor vehicle. The line sections assigned to the voltage converter include, for example, feed lines to the voltage converter and lines arranged between the voltage converter and the respective electric consuming device supplied by it.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.